The present invention is related to methods and tools used for treating and in particular cleaning and drying surfaces of substrates such as semiconductor substrates used in the production of integrated circuits or flat panel displays, and equally of foil like substrates or wires.
The complete and efficient removal of a liquid from a surface of a substrate is a frequently repeated step in e.g. the fabrication process of integrated circuits. Such a step can be performed after a wet etching step, a wet cleaning step, a wet rinsing step or any other step used in the fabrication process wherein a substrate is treated by, exposed to or immersed in a liquid. The substrate can be a semiconductor wafer or a part thereof or a glass slice or any other slice of material. It can also be a continuous film or foil or a wire or a set of parallel wires.
The manufacturing of integrated circuits evolves towards processing of each wafer individually rather than in batches of several wafers. In state of the art IC manufacturing, most processing steps such as e.g. implantation steps or deposition steps are already performed in a single wafer mode. On the other hand, wet processing steps such as e.g. cleaning steps and subsequent liquid removal steps are typically performed in a batch mode because of lack of appropriate alternatives. Therefore, differences in waiting times are created for each individual wafer between a wet processing step, performed in a batch mode and another processing step, performed in a single wafer mode. Such variability is undesirable with regard to process control. Moreover, this mixed batch and single wafer processing increases the cycle time, which is also undesirable. Therefore, there is a general interest in the development of competitive single wafer or more generally, single substrate wet processing steps. Also, a method for treating and drying continuous foil or film like substrates and wire-like substrates is not present in the current state of the art.
With regard to the drying process, simultaneous drying of both sides of a substrate is desired in a reduced timespan. Knowing that in state of the art production lines a substrate is processed typically every 1 to 2 minutes, ideally, in order to avoid equipment duplication, the combined liquid process step and liquid removal step should be completed in at least such a time frame.
The principle of immersing a substrate in a treatment liquid and subsequently removing said substrate in such a way that a minimum of liquid remains attached to the substrate, is known. However, all existing methods and tools based on this principle possess fundamental drawbacks.
In the document EP-A-385536, a method is disclosed of drying substrates after treatment in a liquid by pulling said substrates out of a tank containing said liquid. While being slowly taken from the tank, the substrates are brought directly in contact with a vapor which is miscible with said liquid. When mixed with the liquid, the mixture has a surface tension lower than that of the liquid, i.e. the vapor works as a xe2x80x98tensio-activexe2x80x99 gaseous substance.
An important drawback of the method described in EP-A-385536 relates to the fact that virtually all the liquid in the tank must remain there after the substrates have been removed, which implicates that pulling the substrates out of the liquid must take place slowly. As a consequence, this method is typically applied to the simultaneous treatment of batches of substrates in order to meet throughput requirements. The flow of the tensio-active vapor is provided through two sets of nozzles, one set on each side of a substrate, causing two opposite flows of vapor, colliding in the middle of the substrate. As a result, in this middle part, drying will be less efficient than at the substrate""s edges.
In document EP-A-817246, a method and apparatus is described for wet cleaning or etching of flat substrates. This document is related to an apparatus comprising a vessel partially filled with a liquid. A substrate is pulled through said stationary liquid by way of slits in the vessel""s sides under the liquid surface. The vessel is placed in a gaseous environment, preferably comprising a tensio-active gas. In this method the wafer is moved preferably horizontally. The horizontal position can be undesirable in terms of tool-footprint minimization or for integration of the drying method with other manufacturing equipment. Besides that, the apparatus described in this document is designed so as to allow no liquid to leave the vessel before, after and most importantly during the transit of the substrates, so as not to wet these substrates. This means that the substrate needs to be removed from the vessel slowly. Because no flow of liquid takes place through the slits, this potentially causes the problem of particle build-up in the slit: small particles become attached to the side walls of the slit and attach to the substrate""s surface as it is passing through. Another drawback is that the slit through which the substrate is removed, is necessarily very narrow (order of 1.5 mm for a 0.75 mm thick substrate). Moreover, narrow horizontal slits are difficult to combine with large substrates (xcfx84 300 mm in diameter), which often suffer from a significant xe2x80x98bowxe2x80x99 phenomenon, i.e. a bending of the central part with respect to the edges, as a result of asymmetric stress, e.g. thermal stress, or simply as an effect of gravity in case of the horizontal or tilted position of substrates.
U.S. Pat. No. 5,660,642 describes an apparatus wherein a substrate is pulled out of a tank, while being sprayed with a liquid inside said tank, above a stationary liquid surface. A porous medium or other solvent vapor source is placed around the opening through which the substrate is pulled out, and produces vapors to be adsorbed by the substrate in order to remove liquid attached to it. No liquid is allowed to flow out of said tank while the substrate is being pulled out. Also, no flow of a tensio-active gas is directed at the substrate, which is merely passively brought into contact with a vapor, not a flow of vapor. This necessarily puts a constraint on the allowable removal speed of the substrate, which renders this technique unable to fulfill current treatment speed requirements. Also, a spray is often undesirable, as it deteriorates the subsequent drying performance: after spraying, residues can be detected (with reactive light scattering inspection techniques) on the surface, e.g. on hydrophobic surfaces sprayed with water, when the drying step is completed.
Document DE-A-4413077 describes a method and apparatus for treating and/or cleaning and drying a substrate, by lifting said substrate or preferably a batch of substrates, out of a cylindrical bath. Liquid is allowed to flow over the edge of said bath during the removal of the substrate. The substrate may be lifted out of the bath and into an enclosure filled with a tensio-active gas, for drying the substrate. Once again, this passive contact with a tensio-active gas is detrimental for efficient and especially for fast drying.
A drawback of many of the existing tools and methods is the necessary footprint, i.e. the surface in the clean room occupied by a tank or a vessel. Tools that work with batches of substrates or which handle individual substrates in a horizontal position tend to occupy a large area in the clean room, which results in high costs, since clean room space is very expensive due to the costs of maintaining an ultra-pure atmosphere.
Document WO-A-99/08057 describes another method and apparatus for drying a substrate. The apparatus comprises a tank. The substrate can be held in the tank by a holder at different holding points. The tank comprises a fluid. The substrate is dried by lowering the level of fluid in the tank relatively to the stationary substrate. A flow of a tensio-active vapor is directed parallel to the substrate and the fluid surface. U.S. Pat. No. 5,571,337 equally describes a method wherein a liquid level is lowered. This lowering of a liquid level relative to a stationary substrate has some disadvantages. Particles removed from the substrate surface will tend to gather near the liquid surface, so a risk appears of contaminating substrates, if the liquid is not replaced in time. Also, if a gaseous environment or flow is used above a stationary liquid surface, this liquid will become saturated with the gas, reducing the drying effect exerted by the gas.
Finally, lowering a liquid is a technique which is unsuitable for the treatment and drying of continuous substrates, such as foils, film, tape or wire.
A final problem in many existing methods and tools is the fact that a droplet of liquid remains attached to the part of the substrate which is last removed from the liquid. To this problem, no satisfactory solution has so far been proposed.
The present invention aims to propose a method and apparatus allowing the efficient and fast removal of liquid from both surfaces of a substrate.
In particular, the present invention aims to propose a method and apparatus for liquid removal, including the last droplet.
The present invention is related to a method for performing a liquid treatment on at least one substrate, including the removal of a liquid from at least one flat surface of said substrate, said method comprising the following steps:
introducing said substrate in a tank,
filling said tank with a liquid, said step of filling said tank taking place before or after said step of introducing said substrate,
performing at least one liquid treatment step on said substrate,
removing said substrate from said tank in an essentially vertical direction, said direction being parallel to said substrate surfaces that are to be dried, through an opening in the top part of said tank, so that a liquid flow out of said tank is produced between said substrate and said opening during the passage of said substrate through said opening,
According to one preferred embodiment, simultaneously with said step of removing said substrate, the step of directing a flow of a gaseous substance at the intersection line between a substrate surface that is to be dried, and said liquid, in such a way that the plane comprising both the speed vector of the substrate movement and of said flow of a gaseous substance is perpendicular to the surface of said substrate that is to be dried.
According to another preferred embodiment, said substrate has parallel flat surfaces, and said flow of a gaseous substance is produced through a narrow opening of a device positioned in such a way that said narrow opening is parallel to said flat surfaces, and wherein the speed, pressure and direction of said flow is equal in each point of said narrow opening.
According to the invention, said gaseous substance is part of the group consisting of a non-heated tensio-active gas, a heated tensio-active gas, a non-heated tensio-active vapor, a heated tensio-active vapor, a heated inert gas, or a mixture of at least two of the preceding gaseous substances.
Secondly, the invention is related to a method for performing a liquid treatment on at least one substrate including the removal of a liquid from at least one surface of said substrate, said method comprising the following steps:
introducing said substrate in a tank,
filling said tank with a liquid, said step of filling said tank taking place before or after said step of introducing said substrate
performing at least one liquid treatment step on said substrate,
removing said substrate from said tank in an essentially vertical direction, said direction being parallel to said substrate surfaces that are to be dried, through an opening in the top part of said tank, so that a liquid flow out of said tank is produced between said substrate and said opening during the passage of said substrate through said opening,
According to a preferred embodiment, simultaneously with said step of removing said substrate, the step of directing a heat supply at the intersection line between a substrate surface that is to be dried, and said liquid, said heat supply being produced along a line perpendicular to the substrate movement, in such a way that the same heat is produced in every point of said line.
According to another preferred embodiment, when said substrate has two parallel flat surfaces, during the removal of said substrate, a flow of liquid takes place between said flat surfaces and the sides of said opening neighboring said flat surfaces, so that in at least one cross section perpendicular to the substrate surfaces, said flow is uni-directional and essentially non-turbulent.
In the method of the invention for cleaning with water and drying a hydrophilic silicon substrate at room temperature, the speed at which the substrate is removed from the liquid is constant and at least equal to 15 mm/s.
The speed at which the substrate is removed from the liquid may also be reduced prior to the moment when the last part of the substrate passes through the opening.
The method according to the invention may further comprise the step of bringing the last part of said substrate that leaves said liquid into contact with an object, in order to remove a last droplet attached to said last part.
The method according to the invention may further comprise the step of holding said substrate after removal from said substrate from said tank, and directing a flow of a gaseous substance essentially parallel to the surfaces of said substrate that are to be dried.
The present invention is equally related to an apparatus for liquid treating and drying at least one flat substrate, in particular a semiconductor substrate, according to the method of the invention, said apparatus comprising:
a tank, said tank comprising in its wall at least one hole and comprising at least one opening in a top section of said tank, said opening allowing the passage of said substrate in a direction parallel to the plane of said substrate, said tank on the outside further comprising a gutter and a drain, the gutter on at least a portion of the tank (and in one embodiment surrounding the tank), the drain connected to said gutter,
means for moving said substrate into said tank, and means for moving said substrate out of said tank through said opening in a substantially vertical direction.
The apparatus may further comprise a means for directing a flow of a gaseous substance at at least one intersection line between a substrate and a liquid present in said tank, as said substrate is moved out of said tank through said opening, said flow having essentially the same speed and pressure in every point along said intersection line.
Alternatively, instead of said means for directing a flow of a gaseous substance, an apparatus of the invention may comprise means for directing a heat supply at at least one intersection line between said substrate and a liquid present in said tank, as said substrate is moved out of said tank through said opening, said heat supply having essentially the same intensity in every point along said intersection line.
In an apparatus according to the invention, wherein one substrate is treated, the sides of said opening are preferably parallel to said substrate and the width of said opening is at least twice the thickness of said substrate.
In an apparatus according to the invention, the top part of the tank forms a converging channel wherein a liquid may flow out of the tank and towards said opening.
Said means for directing a flow of gaseous substance may comprise at least one nozzle producing said flow of gaseous substance through a narrow slit which is essentially parallel to said intersection line and whose length is at least equal to that of said intersection line.
An apparatus according to the invention may further comprise a container placed above said tank, said container comprising an opening at its bottom, i.e. facing said opening of said tank, so that a substrate can move along a straight line from said tank to said container through said openings, said container further comprising at least one inlet opening for letting in a flow of a gaseous substance.
Preferably, in said last embodiment, a first gaseous substance is introduced in said container through at least one first hole in the top part of said container and wherein a second gaseous substance is introduced through at least one long and narrow opening in the lower part of at least one side wall of said container, said long and narrow opening being pointed downwards, i.e. in the direction of the tank, and wherein the part of the container under said at least one long and narrow opening forms a channel with a converging width, as seen in a cross section perpendicular to the center line of the openings through which the substrate moves.
An apparatus using a gas flow for drying may further comprise an exhaust channel for removing said gaseous substance from said intersection line between said substrate and said liquid. The sides of said exhaust channel may be sealed off from the surrounding atmosphere.
According to another embodiment, said substrate may be flexible and continuous, and said tank may then comprise at least one transporting device, such as a roller, for transporting said flexible substrate through a liquid inside said tank. In this embodiment, the substrate may be a film, foil, tape or wire.
According to an embodiment of the invention, an apparatus is proposed using the method of the invention for treating and drying a batch of parallel flat substrates and comprising a tank, at least one gutter, and at least one drain, wherein said liquid flows out of said tank only between the short edges of said substrates and the neighboring sides of said tank.
An apparatus according to the invention may further comprise means for removing a last droplet attached to the last part of said substrate that leaves said liquid, said means for removing a last droplet being chosen from the group consisting of:
At least one fiber attached to the top part of said tank,
At least one piece of foam attached to the top part of said tank.